redirect to another pool when primary pool unavailable.

So just curious, but why do you have this http class applied if you have the pool defined in the VIP? Can I assume your intention here is to direct traffic to the prod pool if the host matches "mysite.com"?

Also check /var/log/ltm for any errors. An iRule error will usually manifest as a bad response in the browser, and you should see something in the log.

Worst case the pool selection could be working but the sorry server is sending something the browser doesn't understand. Performing a client side capture to see if you you're actually seeing HTTP payload from the sorry server might help.